[svt] Add support for TV channel live streams (Closes #15279)

[0x9fff00]

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Description of your pull request and other information

Add support for the live streams of the SVT channels on SVT Play.
Example: https://www.svtplay.se/kanaler/svt1

[dstftw]

1. Live streams must have _live_title as title and is_live set appropriately.
2. HLS live formats must be processed by ffmpeg.

[0x9fff00]

I've updated the commit to include those changes now.